I received your Private Message on this question.Motors are powered by pulsed currents from the circuit boards to control rpm -- Pulse Width Modulation (PWM). The components can reverse a motor by changing the polarity of the voltage. Note how the drive wheel motors can move both forwards and backwards.The software and the computer controls the motor drive components. Special IC's may be used to drive the motors. It is difficult to indentify which circuit component is defective without the circuit design schematic diagrams and part specifications. Expert engineers might be able to trace the circuits.The computer software may have an error. Parts and circuit boards are available at samsungparts.com. For such an old device it may not be economical to replace many parts.The wires to the motor might be examined with a volt meter to observe whether the polarity is being reversed.

It is theoretically possible the software reverses the brush motor in response to some obstacle or blockage stopping the brush. The computer senses the motor rpm and detects when the brush is blocked. Error messages are displayed for such blockage. The software might use a strategy of reversing the motor to possibly eject blocking debris.A defective motor or drive belt slipping might cause a stoppage to be detected and trigger the software and error message. The details of the motor use is not published by Samsung. There could be dirt in the drive belt assembly blocking the motor. Drive belts can wear out. Examine all the parts.

- completely cleaned the drum unit.- Measured the motor in the test mode - there is a reversal of the voltages.

The following considerations from me:The engine must have a "speedometer" to report its revolutions to the board?!?! Maybe this is broken.The board has a defective component in the area of the motor control (FDS4897C and 74HC08A).The software is buggy.

A defect in the rpm sensor on the motor would report false blockages to the cpu.The sensor signal could be analyzed with instruments, maybe a frequency scale on multimeter,oscilloscope. Not an engineer. Sensor usually a magnetic disk and detector.

Roomba's had a feature to reverse the brush to eject cables on the floor picked up.

The RPM sensor for the motor or the circuit connected could be at fault. A false blockage could be detected, causing a reversal of direction to eject debris.Robots can be supported on books with the wheels free to observe motor operation. In some robots the suspension arm must be taped down to prevent activating a switch sensing lifting the robot off the floor.